1. Field of the Invention
The present invention relates to arylglyoxals (such as substituted and unsubstituted phenylglyoxals) and, more particularly, to a method for the preparation thereof. Still more particularly, the present invention discloses methods for preparing arylglyoxals (such as substituted and unsubstituted phenylglyoxals) from corresponding arylketones (such as substituted and unsubstituted acetophenones).
2. Description of the Prior Art
The following prior art references are disclosed in accordance with the terms of 37 CFR 1.56, 1.97, and 1.93.
Substituted phenylglyoxals such as hydroxyphenylglyoxal (hereinafter referred to sometimes as "HPGO") are well-known compounds that are useful in the production of intermediate products which are utilized for the preparation of pharmaceutical products. In Organic Syntheses, Coll Vol. 2, A. Blatt, edd., (1943) at p. 509, a method is disclosed for the production of unsubstituted phenylglyoxals from an acetophenone. That method uses the toxic substances selenium dioxide (SeO.sub.2) thereby posing undesirable health hazards and disposal problems.
D. T. Manning and H. A. Stansbury, Jr., J. Am. Chem. Soc., 81, 4885-90 (1959) discloses the reaction of an unsubstituted acetophenone with nitrosyl chloride in ethanol to give a 12.4 percent yield of phenylglyoxal diethyl acetal. In addition, other reaction products are generated in that reaction.
U.S. Pat. No. 4,013,680 discloses a two-step method for the preparation of .alpha.-keto acids such as phenylglyoxylic acid by the oxidation of methyl ketones in aqueous solution with an inorganic nitrite salt and hydrochloric or sulfuric acid. It suggests that the reaction proceeds via the formation of a glyoxal intermediate.
U.S. Pat. No. 4,272,453 discloses a method for the preparation of 1-chloro-1-p-methoxybenzoylformaldoxime by the addition of p-methoxyacetophenone to nitrosyl chloride in carbon tetrachloride.
U.S. Pat. No. 3,794,620 discloses the reaction of nitrosyl chloride with aromatic acetyl derivatives. According to that patent, three moles of nitrosyl chloride are required for each acetal group.
German Patent DE 2,432,563 discloses the oxidation of substituted acetophenones using alkyl nitrites in alcohol and hydrochloric acid to prepare substituted phenylglyoxalacetals.
German Patent DE 3,539,629 discloses a method of oxidizing substituted acetophenones using dinitrogen trioxide in alcohol/hydrochloric acid to prepare appropriate substituted phenylglyoxal acetals.
U.S. Pat. No. 5,124,489 discloses the reaction of a substituted acetophenone with a primary or a secondary alcohol in the presence of a source of a hydrogen ion (H.sup.+) and a source of a nitrosonium ion (NO.sup.+) to form a corresponding substituted phenylglyoxalacetal. That patent however, does not disclose the formation of the substituted phenylglyoxal.
The present invention discloses an improved method for the preparation of arylglyoxals such as a substituted or an unsubstituted phenylglyoxal from a corresponding arylketone such as a substituted or unsubstituted acetophenone. The method involves fewer steps for the addition of reactants, avoids the use of toxic materials and complicated extraction procedures, and provides for the reaction to be carried out in one reactor.
These and other advantages and objects of the present invention will become apparent from the following description.
All of the above-cited prior art and any other references mentioned herein are incorporated herein by reference in their entirety.